The Protein Skimmer – What Is Wet And Dry Foam?

In a saltwater aquarium there are various devices that are designed to assist in the maintenance of high quality seawater. Perhaps the most useful of these is the protein skimmer (ignoring bio-filtration).

As with all devices for it to be at its most effective it must be adjusted correctly. First though, the skimmer must be appropriate to the size of the system.

The normal way of sizing a skimmer is to simply double the net gallonage of the entire system, then find a skimmer that can deal with about that amount. This is a guideline only, and is designed to overcome the sometimes optimistic claims of manufacturers. As long as the skimmer is not a long way short of the guideline it should suffice. Having said that, some manufacturers seem to be more realistic of late with the potential performance of their skimmers.

Skimmers are available as ‘hang-on’ and stand alone, and it is the aquarist who decides which is the most practical. For example, if there isn’t a sump then a ‘hang-on’ is probably the best choice.

It is also important to ensure as far as possible that the model chosen is a good one. Internet forums are useful for this, though there are likely to be some differences in opinion. Maybe more useful, sometimes a local retailer has hobby-sized skimmers running on aquariums, and these can be judged quite easily. First of all, look at the chamber where the bubble/water interaction takes place. The bubbles should be very small and in very great numbers – the bubble chamber should be full of them and coloured white (ish). One respected manufacturer states that the important things about a skimmer are ‘design, air output, air output, and air output.’ Also look at the collection cup, hopefully the skimmate (the dirty liquid inside) will be dark coloured. (This colouration has a lot to do with the way a skimmer is set-up and the amount of dissolved organics available, so a visual check is not entirely reliable.)

So the foam. This is the foam that forms at the surface of the bubble chamber and rises up the throat towards the collection cup. In a badly set skimmer, foam rises very rapidly in the throat and dribbles nearly continuously into the collection cup. The foam can be seen to collapse immediately or nearly so. The skimmate collected is weak in colour and thin. The cause of this is usually the bubble setting, where the amount of bubbles being produced is too high. This is the so-called wet foam.

At the other end, the foam may not rise very much at all, but when any gets into the collection cup it is thick and dark. The foam can be seen to be stiff, and is very slow to collapse. In this case, the setting is not far from being correct. This is the so-called dry foam.

The general ideal is where the settings produce many bubbles, but the foam does not get into the collection cup all the time. The foam may rise up the throat only to fall back when the rise begins again, and it is stiff and not too quick to collapse. When dissolved organics are present, the foam rises and enters the collection cup readily. It is dark, thick and can be smelly.

The manufacturer’s instructions should be followed initially, setting the device as suggested. Make sure the foam does not flow into the collection cup too rapidly, but allow the skimmer time to settle for a few days, as foam production is often affected by the manufacturing process. Once this time period has passed, trial and error will show the best settings for an individual aquarium. There needs to be good bubble production, which is controlled by the air intake setting, balanced with the appropriate flow rate.

A skimmer does not usually produce skimmate continuously, but will react to any dissolved organics. Some additives cause a reaction, and the addition of foods, such as some frozen types, usually will too.

Once the settings have been arrived at, usually they can be left alone. It is important to clean the throat (and collection cup) of the skimmer, as the sludge in the throat will adversely affect performance. When cleaning is done, skimmers often needs a short settling period again before full performance returns.

Well I don’t know, blue stuff! The skimmer is operating correctly as its collecting the ‘normal’ residue, the brown ‘orrible yuk that accumulates in the neck and waste receptacle, so the skimmer isn’t at fault. Perhaps its the last of the factory left stuff which will go away after a little while longer – brand new skimmers usually don’t operate at peak efficiency until after a short period. If all seawater parameters are as they should be and provided the livestock are showing no signs of discomfort a longer wait shouldn’t cause any problem.